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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="../welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="../setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="../postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="../reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="../setup/forward_proxy.html">Configuring a Forward/Outbound Proxy</a></li><li class="chapter-item expanded "><a href="../turn-howto.html">Configuring a Turn Server</a></li><li class="chapter-item expanded "><a href="../delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a 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FAQ</a></li><li class="chapter-item expanded "><div>Scripts</div></li></ol></li><li class="chapter-item expanded "><li class="part-title">Development</li><li class="chapter-item expanded "><a href="../development/contributing_guide.html">Contributing Guide</a></li><li class="chapter-item expanded "><a href="../code_style.html">Code Style</a></li><li class="chapter-item expanded "><a href="../development/git.html">Git Usage</a></li><li class="chapter-item expanded "><div>Testing</div></li><li class="chapter-item expanded "><a href="../opentracing.html">OpenTracing</a></li><li class="chapter-item expanded "><a href="../development/database_schema.html" class="active">Database Schemas</a></li><li class="chapter-item expanded "><a href="../development/experimental_features.html">Experimental features</a></li><li class="chapter-item expanded "><div>Synapse Architecture</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="../log_contexts.html">Log 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<h1 id="synapse-database-schema-files"><a class="header" href="#synapse-database-schema-files">Synapse database schema files</a></h1>
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<p>Synapse's database schema is stored in the <code>synapse.storage.schema</code> module.</p>
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<h2 id="logical-databases"><a class="header" href="#logical-databases">Logical databases</a></h2>
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<p>Synapse supports splitting its datastore across multiple physical databases (which can
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be useful for large installations), and the schema files are therefore split according
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to the logical database they apply to.</p>
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<p>At the time of writing, the following "logical" databases are supported:</p>
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<ul>
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<li><code>state</code> - used to store Matrix room state (more specifically, <code>state_groups</code>,
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their relationships and contents).</li>
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<li><code>main</code> - stores everything else.</li>
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</ul>
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<p>Additionally, the <code>common</code> directory contains schema files for tables which must be
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present on <em>all</em> physical databases.</p>
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<h2 id="synapse-schema-versions"><a class="header" href="#synapse-schema-versions">Synapse schema versions</a></h2>
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<p>Synapse manages its database schema via "schema versions". These are mainly used to
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help avoid confusion if the Synapse codebase is rolled back after the database is
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updated. They work as follows:</p>
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<ul>
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<li>
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<p>The Synapse codebase defines a constant <code>synapse.storage.schema.SCHEMA_VERSION</code>
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which represents the expectations made about the database by that version. For
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example, as of Synapse v1.36, this is <code>59</code>.</p>
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</li>
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<li>
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<p>The database stores a "compatibility version" in
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<code>schema_compat_version.compat_version</code> which defines the <code>SCHEMA_VERSION</code> of the
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oldest version of Synapse which will work with the database. On startup, if
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<code>compat_version</code> is found to be newer than <code>SCHEMA_VERSION</code>, Synapse will refuse to
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start.</p>
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<p>Synapse automatically updates this field from
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<code>synapse.storage.schema.SCHEMA_COMPAT_VERSION</code>.</p>
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</li>
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<li>
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<p>Whenever a backwards-incompatible change is made to the database format (normally
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via a <code>delta</code> file), <code>synapse.storage.schema.SCHEMA_COMPAT_VERSION</code> is also updated
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so that administrators can not accidentally roll back to a too-old version of Synapse.</p>
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</li>
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</ul>
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<p>Generally, the goal is to maintain compatibility with at least one or two previous
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releases of Synapse, so any substantial change tends to require multiple releases and a
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bit of forward-planning to get right.</p>
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<p>As a worked example: we want to remove the <code>room_stats_historical</code> table. Here is how it
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might pan out.</p>
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<ol>
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<li>
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<p>Replace any code that <em>reads</em> from <code>room_stats_historical</code> with alternative
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implementations, but keep writing to it in case of rollback to an earlier version.
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Also, increase <code>synapse.storage.schema.SCHEMA_VERSION</code>. In this
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instance, there is no existing code which reads from <code>room_stats_historical</code>, so
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our starting point is:</p>
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<p>v1.36.0: <code>SCHEMA_VERSION=59</code>, <code>SCHEMA_COMPAT_VERSION=59</code></p>
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</li>
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<li>
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<p>Next (say in Synapse v1.37.0): remove the code that <em>writes</em> to
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<code>room_stats_historical</code>, but don’t yet remove the table in case of rollback to
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v1.36.0. Again, we increase <code>synapse.storage.schema.SCHEMA_VERSION</code>, but
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because we have not broken compatibility with v1.36, we do not yet update
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<code>SCHEMA_COMPAT_VERSION</code>. We now have:</p>
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<p>v1.37.0: <code>SCHEMA_VERSION=60</code>, <code>SCHEMA_COMPAT_VERSION=59</code>.</p>
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</li>
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<li>
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<p>Later (say in Synapse v1.38.0): we can remove the table altogether. This will
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break compatibility with v1.36.0, so we must update <code>SCHEMA_COMPAT_VERSION</code> accordingly.
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There is no need to update <code>synapse.storage.schema.SCHEMA_VERSION</code>, since there is no
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change to the Synapse codebase here. So we end up with:</p>
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<p>v1.38.0: <code>SCHEMA_VERSION=60</code>, <code>SCHEMA_COMPAT_VERSION=60</code>.</p>
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</li>
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</ol>
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<p>If in doubt about whether to update <code>SCHEMA_VERSION</code> or not, it is generally best to
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lean towards doing so.</p>
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<h2 id="full-schema-dumps"><a class="header" href="#full-schema-dumps">Full schema dumps</a></h2>
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<p>In the <code>full_schemas</code> directories, only the most recently-numbered snapshot is used
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(<code>54</code> at the time of writing). Older snapshots (eg, <code>16</code>) are present for historical
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reference only.</p>
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<h3 id="building-full-schema-dumps"><a class="header" href="#building-full-schema-dumps">Building full schema dumps</a></h3>
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<p>If you want to recreate these schemas, they need to be made from a database that
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has had all background updates run.</p>
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<p>To do so, use <code>scripts-dev/make_full_schema.sh</code>. This will produce new
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<code>full.sql.postgres</code> and <code>full.sql.sqlite</code> files.</p>
|
||
<p>Ensure postgres is installed, then run:</p>
|
||
<pre><code class="language-sh">./scripts-dev/make_full_schema.sh -p postgres_username -o output_dir/
|
||
</code></pre>
|
||
<p>NB at the time of writing, this script predates the split into separate <code>state</code>/<code>main</code>
|
||
databases so will require updates to handle that correctly.</p>
|
||
<h2 id="boolean-columns"><a class="header" href="#boolean-columns">Boolean columns</a></h2>
|
||
<p>Boolean columns require special treatment, since SQLite treats booleans the
|
||
same as integers.</p>
|
||
<p>There are three separate aspects to this:</p>
|
||
<ul>
|
||
<li>
|
||
<p>Any new boolean column must be added to the <code>BOOLEAN_COLUMNS</code> list in
|
||
<code>scripts/synapse_port_db</code>. This tells the port script to cast the integer
|
||
value from SQLite to a boolean before writing the value to the postgres
|
||
database.</p>
|
||
</li>
|
||
<li>
|
||
<p>Before SQLite 3.23, <code>TRUE</code> and <code>FALSE</code> were not recognised as constants by
|
||
SQLite, and the <code>IS [NOT] TRUE</code>/<code>IS [NOT] FALSE</code> operators were not
|
||
supported. This makes it necessary to avoid using <code>TRUE</code> and <code>FALSE</code>
|
||
constants in SQL commands.</p>
|
||
<p>For example, to insert a <code>TRUE</code> value into the database, write:</p>
|
||
<pre><code class="language-python">txn.execute("INSERT INTO tbl(col) VALUES (?)", (True, ))
|
||
</code></pre>
|
||
</li>
|
||
<li>
|
||
<p>Default values for new boolean columns present a particular
|
||
difficulty. Generally it is best to create separate schema files for
|
||
Postgres and SQLite. For example:</p>
|
||
<pre><code class="language-sql"># in 00delta.sql.postgres:
|
||
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT FALSE;
|
||
</code></pre>
|
||
<pre><code class="language-sql"># in 00delta.sql.sqlite:
|
||
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT 0;
|
||
</code></pre>
|
||
<p>Note that there is a particularly insidious failure mode here: the Postgres
|
||
flavour will be accepted by SQLite 3.22, but will give a column whose
|
||
default value is the <strong>string</strong> <code>"FALSE"</code> - which, when cast back to a boolean
|
||
in Python, evaluates to <code>True</code>.</p>
|
||
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|
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